The invention relates to the labeling of objects by the use of heat to transfer designs from a carrier and, more particularly, to labeling which is resistant to objectionable discoloration, cracking and crawling during the heat transfer process.
In heat transfer labeling a design in a transfer layer is brought into contact with the object to be labeled. The transfer layer is usually held on a carrier by a release layer. When heat is applied to the carrier, the release layer becomes molten and releases the transfer layer and the accompanying design.
In the case of some heat transfer labels, such as those exemplified by U.S. Pat. No. 3,516,904, which issued to John J. Klinker on June 23, 1970, the release layer is of oxidized polyethylene. This kind of release layer is objectionable because it produces discolored, i.e., yellowed, heat transfer decorations. The transferred decorations also tend to be "hazy".
In other cases, such as exemplified by U.S. Pat. No. 3,516,842, which also issued to John J. Klinker et al. on June 23, 1970, the release layer can be of unoxidized polyethylene or a blend of ethyl-vinyl acetate copolymer and paraffin wax. The release layer produces objectionable cracking and crawling.
The cracking and crawling are caused by the differential expansion that takes place between an underlying wax-like release layer and an overlying design print in a transfer layer. When the two layers expand unevenly upon heating, they tend to separate from one another by forming ridges or corrugations where portions of one layer have separated from an adjoining layer. The result is a set of pressure ridges that break when stress is relieved. The resulting transferred label is unsightly and generally unsatisfactory.
Accordingly, it is an object of the invention to reduce discoloration in crawl and crackage resistant release layers.
Another object of the invention is to reduce the amount of haziness and cloudiness that often accompanies the use of synthetic wax-like materials in transfer layers.